Please help with chemistry question!!!

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Minnie16
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Name:  chem.PNG
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Size:  47.8 KBCan someone please explain why the answers to these questions are A, C and D
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Rleggett12
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I'm guessing that Acid P and base X is A because the acid is strong (Low pH) and the base is strong (High pH) so the pHs of the acid and base must be the range stated in the question meaning both indicators give a precise end point (of the titration).

Then Acid Q (weak, neutral pH) and base X (strong, high pH) is C because the phenolphthalein gives an endpoint of the titration because the base is in the pH range stated in the question but the weak Acid is not within the pH range of methyl orange so it does not give a precise endpoint.

Then Acid Q (weak, neutral pH) and base Y (weak, neutral pH) is D because the more neutral pHs of these substances means they are out of the ranges of the testers stated in the question so will not give a precise end point.

(Sorry if any of this is wrong I'm only at GCSE level but got an A* in my chemistry GCSE last year - doing triple)
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Minnie16
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(Original post by Rleggett12)
I'm guessing that Acid P and base X is A because the acid is strong (Low pH) and the base is strong (High pH) so the pHs of the acid and base must be the range stated in the question meaning both indicators give a precise end point (of the titration).

Then Acid Q (weak, neutral pH) and base X (strong, high pH) is C because the phenolphthalein gives an endpoint of the titration because the base is in the pH range stated in the question but the weak Acid is not within the pH range of methyl orange so it does not give a precise endpoint.

Then Acid Q (weak, neutral pH) and base Y (weak, neutral pH) is D because the more neutral pHs of these substances means they are out of the ranges of the testers stated in the question so will not give a precise end point.

(Sorry if any of this is wrong I'm only at GCSE level but got an A* in my chemistry GCSE last year - doing triple)
The part I get confused with is that I was told that a strong Base pH is equal or above 11 and and strong acid pH is equal to or below 3.

But according to the answers, they suggest that a strong acid has a pH above 3 and a strong base has a pH of below 10. This goes against what I've been taught. Is my book wrong or am I misunderstanding something?
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Rleggett12
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(Original post by Jas1947)
The part I get confused with is that I was told that a strong Base pH is equal or above 11 and and strong acid pH is equal to or below 3.

But according to the answers, they suggest that a strong acid has a pH above 3 and a strong base has a pH of below 10. This goes against what I've been taught. Is my book wrong or am I misunderstanding something?
Sorry, my explanation might be confusing, because the pH of the strong acid is outside that range it gives a precise end point, and opposite for bases (above 10 = precise end point and strong base)
think I got confused with that point!
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Minnie16
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(Original post by Rleggett12)
Sorry, my explanation might be confusing, because the pH of the strong acid is outside that range it gives a precise end point, and opposite for bases (above 10 = precise end point and strong base)
think I got confused with that point!
No I don't understand. Here's how I am thinking, let's use (iii) as an example. Let's say acid Q has a pH of 4 and base Y has a pH of 9. Because these pHs are already in the range of both indicators therefore both indicators will change colour as soon as they're put in the solution. They change colour before the two solutions are even mixed? Is this right?
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Rleggett12
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(Original post by Jas1947)
No I don't understand. Here's how I am thinking, let's use (iii) as an example. Let's say acid Q has a pH of 4 and base Y has a pH of 9. Because these pHs are already in the range of both indicators therefore both indicators will change colour as soon as they're put in the solution. They change colour before the two solutions are even mixed? Is this right?
1. I don't believe there is only 1 mark for each part

2. Q and Y would have more neutral pHs (more like 4/8) which are inside those ranges.

3. I think that the indicators are used whilst they are mixing (titrating, Spelling?) so that's why they both give a precise end point, when the colours become neutral pH
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Cave Felem
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1) A
2) C
3) D

This is a pH curve question. You need the equivalence point of each titration to fall within the range of given indicator in order for the indicator to be accurate. Strong acid with strong base allows any indicator to be used as the pH curve is very steep, hence A. 2 is only phenolphthalein because methyl orange's pH range would not include the equivalence point (look up the titration curve for strong base weak acid). Lastly, indicators cannot be used in a titration between a weak acid and weak base because there is not an easily defined equivalence point. Hope this helps!
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Cave Felem
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(Original post by Rleggett12)
I'm guessing that Acid P and base X is A because the acid is strong (Low pH) and the base is strong (High pH) so the pHs of the acid and base must be the range stated in the question meaning both indicators give a precise end point (of the titration).

Then Acid Q (weak, neutral pH) and base X (strong, high pH) is C because the phenolphthalein gives an endpoint of the titration because the base is in the pH range stated in the question but the weak Acid is not within the pH range of methyl orange so it does not give a precise endpoint.

Then Acid Q (weak, neutral pH) and base Y (weak, neutral pH) is D because the more neutral pHs of these substances means they are out of the ranges of the testers stated in the question so will not give a precise end point.

(Sorry if any of this is wrong I'm only at GCSE level but got an A* in my chemistry GCSE last year - doing triple)
The right answer but the wrong logic, because you haven't studied pH curves yet.
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Rleggett12
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(Original post by Cave Felem)
The right answer but the wrong logic, because you haven't studied pH curves yet.
Ah, ok thanks! I did finish my chemistry GCSE and got an A* so thought I could test myself by helping 😂 Thank you for clearing things up! 👍🏻
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Rleggett12
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(Original post by Jas1947)
No I don't understand. Here's how I am thinking, let's use (iii) as an example. Let's say acid Q has a pH of 4 and base Y has a pH of 9. Because these pHs are already in the range of both indicators therefore both indicators will change colour as soon as they're put in the solution. They change colour before the two solutions are even mixed? Is this right?
Sorry about this (I'm only at GCSE level, but wanted to test myself as well by helping) Cave Felem should hopefully make sense to you!
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Minnie16
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(Original post by Rleggett12)
Sorry about this (I'm only at GCSE level, but wanted to test myself as well by helping) Cave Felem should hopefully make sense to you!
Thank you both for your help !
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Rleggett12
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(Original post by Jas1947)
Thank you both for your help !
That's ok😉, sorry about any confusion I gave you 😥
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Minnie16
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(Original post by Rleggett12)
That's ok😉, sorry about any confusion I gave you 😥
No need to apologise, you've actually helped me alot more than my class mates! Keep helping others, you're good at it!
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Rleggett12
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(Original post by Jas1947)
No need to apologise, you've actually helped me alot more than my class mates! Keep helping others, you're good at it!
Thanks! Means a lot to hear that, especially from someone I've never met! 😊
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Sdecicco
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(Original post by Minnie16)
Name:  chem.PNG
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Size:  47.8 KBCan someone please explain why the answers to these questions are A, C and D
Phenolphthalein has a high range for changing colour, so it works with strong alkalis. Methyl orange has a low colour change range so works for strong acids.

If you have strong acid/ alkali, both work. Weak acid/strong alkali - phenolphthalein only. Strong acid, weak alkali - methyl orange only.

If you have a weak acid and weak alkali, there is no equivalence point so indicators can’t be used.
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